Image-forming appratus

ABSTRACT

In an image-forming apparatus such as a printer, the controller judges whether or not a determination processing of fixity saturation state is performed to determine the fixing condition in which the image density of the patch is the fixity saturation state. The controller then performs the determination processing of fixity saturation state when the use condition is changed. The controller settles fixing conditions in which the image density of patch is highest as the set value when the image density of the patch is saturated. Next, the controller performs a toner adhesion amount adjustment using an intermediate transfer belt. A target value of the toner adhesion amount on the intermediate transfer belt corresponding to the target image density is set and then, an optimal developing voltage that is the set target value is set. After the toner adhesion amount adjustment, the controller performs fixity adjustment.

CROSS REFERENCE TO RELATED APPLICATION

The present invention contains subject matter related to Japanese PatentApplication No. JP 2014-25558 filed in the Japanese Patent Office onFeb. 13, 2014, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an image-forming apparatus that formsan image on a sheet.

2. Background Art

An image-forming apparatus adopting an electrophotographic system suchas a printer, a copier, a facsimile and the like has been widely used inthe past. Such an image-forming apparatus has formed toner images ofrespective colors of yellow, cyan, magenta and black on photoreceptorscorresponding to each color and then, it has transferred these tonerimages on an intermediate transfer belt with overlapping them in order.The image-forming apparatus has transferred the transferred toner imageson a sheet being transported at once to form a color image.

In the image-forming apparatus, it has been desirable to keep a toneradhesion amount stable in order to maintain stable an image density ofthe toner image on the sheet. For that purpose, in the image-formingapparatus, a sensor has detected a toner adhesion amount of a patch,which is a toner image for a test and is formed on an image carrier suchas the intermediate transfer belt. Based on this detection resultthereof, the image-forming apparatus has controlled the toner adhesionamount of the image by adjusting any image-forming conditions such ascharged voltages and developing bias voltages.

The image-forming apparatus may generate any failure in the imagedensity by changing, for example, any image-forming conditions in atransfer portion, any fixing conditions in a fixing portion and/or thelike. Accordingly, in recent years, an image-forming apparatus has beendeveloped in which an image density sensor is provided at a downstreamside of the fixing portion and the toner adhesion amount is controlledon the basis of an output of this image density sensor to attainstability in the image density.

Each of Japanese patent application publications Nos. 2007-199466 and2006-171104 discloses the image-forming apparatus which has any facultyto attain stability in the image density. For example, Japanese patentapplication publication No. 2007-199466 discloses the image-formingapparatus which can keep an output image density stable by controlling atarget value of the toner adhesion amount according to a fixingtemperature, a fixing speed and species of sheet. On the other hand,Japanese patent application publication No. 2006-171104 discloses theimage-forming apparatus which adjusts the image density by thedeveloping bias and then, adjusts glossiness by the fixing temperaturewith adding image density value thereto.

SUMMARY OF THE INVENTION Issues to be Addressed by the Invention

However, since a variation in the image density based on the variationin the fixity is adjusted by the toner adhesion amount in theimage-forming apparatus disclosed in each of Japanese patent applicationpublications Nos. 2007-199466 and 2006-171104, the following may occur:Namely, when the fixity of the fixing portion such as the fixingtemperature or pressure (nipping pressure) is excessive or insufficientbased on a variation in use conditions such as exchange of the fixingportion, an individual difference in durability of the fixing portionand the like, the image density may also vary together with such avariation. In each of Japanese patent application publications Nos.2007-199466 and 2006-171104, since the toner adhesion amount is adjustedon the basis of the variation in the image density based on thevariation in the fixity thereof, the toner adhesion amount may beexcessive or insufficient. As a result thereof, when the toner adhesionamount is excessive in the image, this may generate any failures infixing separation and/or in cleaning. When the toner adhesion amount isinsufficient in the image, this may generate any various kinds offailure in density unevenness, deterioration of graininess and the like.

Means for Solving the Issues

This invention addresses the above-mentioned issues and has an object toprovide an improved image-forming apparatus.

To achieve the above-mentioned the object, an image-forming apparatusreflecting one aspect of this invention contains an image-formingportion that forms a patch on a sheet, the patch being a tonner image, afixing portion that fixes the patch formed by the image-forming portionon the sheet, an image-density-detecting portion that detects an imagedensity of the patch fixed by the fixing portion on the sheet, and acontroller that controls the fixing portion to control a toner adhesionamount based on a detection result of the image density of the patch bythe image-density-detecting portion, wherein the controller sets afixing condition of the fixing portion in the control so that the imagedensity of the patch is saturated and controls the fixing portion tocontrol the toner adhesion amount based on the detection result of theimage density of the patch by the image-density-detecting portion, thepatch being formed under the set fixing condition.

It is desirable to provide an image-forming apparatus wherein thecontroller controls the fixing portion to fix plural patches underdifferent fixing conditions, and sets as a set value of the fixingcondition in which the image density of the patch is saturated a fixingcondition in which the image density is highest or approximate to thehighest value of the plural patches detected by theimage-density-detecting portion.

The concluding portion of this specification particularly points out anddirectly claims the subject matter of the present invention. However,those skilled in the art will best understand both the organization andmethod of operation of the invention, together with further advantagesand objects thereof, by reading the remaining portions of thespecification in view of the accompanying drawing(s) wherein likereference characters refer to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration example of an image-formingapparatus according to a first embodiment of this invention;

FIG. 2 is a diagram showing a configuration example of an image densitysensor;

FIG. 3 is a block diagram showing a configuration example of theimage-forming apparatus according to the first embodiment of thisinvention;

FIG. 4 is a graph showing a relationship between a fixing temperatureand the image density in a fixing processing;

FIG. 5 is a graph showing a relationship between the fixing temperatureand a toner adhesion amount in the fixing processing;

FIG. 6 is a flowchart showing an operation example of the image-formingapparatus in a first embodiment of this invention in atoner-adhesion-amount-controlling mode;

FIG. 7 is a flowchart showing an operation example of the image-formingapparatus in a determination processing of fixity saturation state;

FIG. 8 is a flowchart showing an operation example of the image-formingapparatus in a toner adhesion amount adjustment;

FIG. 9 is a flowchart showing an operation example of the image-formingapparatus in a toner adhesion amount adjustment on an intermediatetransfer belt;

FIG. 10 is a flowchart showing an operation example of the image-formingapparatus in a fixity adjustment; and

FIG. 11 is a flowchart showing an operation example of the image-formingapparatus in a second embodiment of this invention during the toneradhesion amount adjustment in the toner-adhesion-amount-controllingmode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe configuration examples of the image-formingapparatus as preferred embodiments relating to the invention withreference to drawings. It is to be noted that the description in theembodiments is exemplified and any technical scope of the claims and/ormeaning of term(s) claimed in the claims are not limited thereto.

First Embodiment [Configuration Examples of Image-Forming Apparatus]

The following will describe the image-forming apparatus 100 according tothe first embodiment of the invention. The image-forming apparatus 100performs a toner-adhesion-amount-controlling process (hereinafter, alsoreferred to as “toner-adhesion-amount-controlling mode”) in a situationwhere an image density of a patch is saturated and prevents a variationin the image density based on a variation in the fixity to accomplish anaccurate control of toner adhesion amount adjustment.

FIG. 1 shows a configuration example of the image-forming apparatus 100according to the first embodiment of this invention. As shown in FIG. 1,the image-forming apparatus 100 is an image forming apparatus called as“tandem type image-forming apparatus”. The image-forming apparatus 100contains an automatic document feeding portion 80 and an apparatus mainbody 102. The apparatus main body 102 mounts the automatic documentfeeding portion 80. The automatic document feeding portion 80 feedssheets set on a document table to an image-reading portion 90 of theapparatus main body 102 using conveying rollers and the like.

The apparatus main body 102 contains a manipulation/display portion 70,the image-reading portion 90, an image-forming portion 10, anintermediate transfer belt (image carrier) 8, an image density control(IDC) sensor 110, a feeder 20, a register unit 200, a fixing portion 44,an image density sensor 120 and an auto duplex unit (ADU) 60.

The manipulation/display portion 70 contains a touch panel in which amanipulation part and a display unit are combined, and various kinds ofoperation keys such as determination keys, a start key and the like,which surround the touch panel. The manipulation/display portion 70displays a menu screen or the like on its screen and receives anyinformation about the image-forming conditions and the fixing conditionsinput by a user through a touch operation on the menu screen and/or anoperation of the operation keys.

The image-reading portion 90 scans and exposes the document mounted onthe document table or the document fed by the automatic document feedingportion 80 using an optical system in a scanning and exposure device.The image reading portion 90 also performs photoelectric conversion on ascanned image of the document by a charge-couple device (CCD) imagesensor to obtain an image information signal. The image-processingportion, not shown, then performs a predetermined processing such as ananalog processing, analog-to-digital (A/D) conversion processing, ashade correction, image compression processing and the like on thisimage information signal and outputs it to the image-forming portion 10.

The image-forming portion 10 forms an image based on anelectrophotographic method. The image-forming portion 10 includes animage-forming unit 10Y which forms a yellow (Y) image, an image-formingunit 10M which forms a magenta (M) image, an image-forming unit 10Cwhich forms a cyan (C) image, an image-forming unit 10K which forms ablack (K) image and secondary transfer rollers (transfer portion) 34. Inthis embodiment, in order to indicate a color relative to commonfunction or name, Y, M, C or K will be attached to the number of thecommon function or name, for example, 10Y, 10M, 10C and 10K.

The image-forming unit 10Y includes a photosensitive drum (imagecarrier) 1Y, a charging portion 2Y arranged around the photosensitivedrum 1Y, a writing (exposure) portion 3Y and a developing portion 4Y.The image-forming unit 10M includes a photosensitive drum (imagecarrier) 1M, a charging portion 2M arranged around the photosensitivedrum 1M, an exposure portion 3M and a developing portion 4M. The imageforming unit 10C includes a photosensitive drum (image carrier) 1C, acharging portion 2C arranged around the photosensitive drum 1C, anexposure portion 3C and a developing portion 4C. The image forming unit10K includes a photosensitive drum (image carrier) 1K, a chargingportion 2K arranged around the photosensitive drum 1K, an exposureportion 3K and a developing portion 4K.

The respective photosensitive drums (image carriers) 1Y, 1M, 1C and 1K,the respective charging portions 2Y, 2M, 2C and 2K, the respectiveexposure portions 3Y, 3M, 3C and 3K and the respective developingportions 4Y, 4M, 4C and 4K of the image forming units 10Y, 10M, 10C and10K have the same configuration as each other. They will be indicated inthe following description with Y, M, C and K being omitted except for acase in which any distinction thereof is required.

Each of the charging portions 2 uniformly charges static charges arounda surface of each of the photosensitive drums 1. Each of the exposureportions 3 contains LED print head (LPH) including LED array and animage-formation lens, and a laser scanning and exposure apparatus withpolygon mirror system. Each of the exposure portions 3 scans each of thephotosensitive drums 1 by laser light based on the image informationsignal to form electrostatic latent images on each of the photosensitivedrums 1. Each of the developing portions 4 develops the electrostaticlatent images formed on each of the photosensitive drums 1 using toners.Thus, a toner image that is visible image is formed on each of thephotosensitive drums 1.

The intermediate transfer belt 8 is an endless belt. The intermediatetransfer belt 8 runs on plural rollers with it being stretched andsupported by them. Together with the rotation of the intermediatetransfer belt 8, each of the primary transfer rollers 7 and each of thephotosensitive drums 1 rotate. When applying a predetermined electricvoltage between each of the primary transfer rollers 7 and each of thephotosensitive drums 1, the toner image formed on each of thephotosensitive drums 1 is transferred on the intermediate transfer belt8 (Primary Transfer). A patch which is a toner image is transferred onthe intermediate transfer belt 8 in a toner-adhesion-amount-controllingmode.

The IDC sensor 110 constitutes an adhesion amount detection portion andis arranged under the photosensitive drum 1K so as to be faced to theintermediate transfer belt 8. The IDC sensor 110 is provided with, forexample, light-emitting device as a source of light and alight-receiving device and irradiates light from the light-emittingdevice to the intermediate transfer belt 8 to receive any lightreflected by an image (patch) on the intermediate transfer belt 8 usingthe light-receiving device. The IDC sensor 110 outputs a voltage valuebased on an amount of received light as a detection value indicating thetoner adhesion amount.

The feeder 20 has plural feeding trays 20A, 20B each containing sheets Pwith a size such as A3, A4 or the like. The feeder 20 feeds the sheets Pone by one from the selected feeding tray 20A or 20B and conveys the fedsheet P to the register unit 200 through conveying rollers 22, 24, 26and 28 and the like. It is to be noted that numbers of the feeding traysare not limited to two. A single or plural large capacity sheetfeeder(s), which can contain a large number of sheets P, may connect theimage-forming apparatus depending on the situation.

The register unit 200 includes a pair of loop-forming rollers 30 and apair of registration rollers 32. The pair of loop-forming rollers 30hits a forward end of the sheet P conveyed by the register unit 200 tothe pair of registration rollers 32 to form a loop so that a skew(inclination) of the sheet P in relation to a sheet-feeding direction Dof the sheet P is corrected. The pair of registration rollers 32 conveysthe sheet P, the skew of which is corrected, to secondary transferrollers 34 at desired timing. The secondary transfer rollers 34 transfertoner images of colors Y, M, C and K transferred on the intermediatetransfer belt 8 altogether to a surface of the sheet P fed by the pairof registration rollers 32 (Secondary Transfer). The secondary transferrollers 34 then conveys the sheet P on which the secondary transfer isformed to the fixing portion 44 that is arranged at a downstream sidealong the sheet-feeding direction D of the sheet P.

The fixing portion 44 contains pressure rollers and heating rollers. Thefixing portion 44 fixes the toner images transferred on the surface ofthe sheet P to the sheet P by applying pressure to the sheet P to whichthe secondary transfer rollers 34 has transferred the toner images andheating the same.

The image density sensor 120 constitutes image-density-detectingportion. The image density sensor 120 is arranged at a downstream sideof the fixing portion 44 along the sheet-conveying direction D. Theimage density sensor 120 measures image density of the patch which isthe toner image fixed on the sheet P. FIG. 2 shows a configurationexample of the image density sensor 120. As shown in FIG. 2, the imagedensity sensor 120 contains a source of light 122 and a light-receivingportion 124. The source of light 122 irradiates light to the fixed patchG on the sheet P. The light-receiving portion 124 receives diffusedlight that is reflected on the patch G and outputs as an image densityvalue the voltage value based on the received light.

A conveying path changeover portion 48 is provided at the downstreamside of the fixing portion 44 along the sheet-feeding direction D. Theconveying path changeover portion 48 performs changeover control of theconveying path based on a selected printing mode (single surfaceprinting mode or duplex printing mode).

Ejection rollers 46 eject onto a sheet-ejection tray, not shown, thesheet P, a single surface of which has been printed in the singlesurface printing mode or both surfaces of which have been printed in theduplex printing mode.

When re-feeding the sheet P, a surface side of which has been printed,to the image forming portion 10 during the duplex printing mode in orderto form an image on a rear surface of the sheet P, the sheet P isconveyed to ADU 60 via the conveying path changeover portion 48. Theconveying rollers 62 and the like convey the sheet P, which is conveyedto the ADU 60, to a switchback route. In the switchback route, ADUrollers 64 perform a reverse rotation control on the sheet P to conveythe sheet P to a U-turn path with a rear end of the sheet P being lead.The conveying rollers 66, 68 and the like provided in the U-turn pathre-feed the sheet P to the pair of registration rollers 32 while frontand back of the sheet P is reversed.

[Configuration Example of Image-Forming Apparatus]

The following will describe a configuration example of the image-formingapparatus 100 according to the first embodiment of the invention withreference to FIG. 3. As shown in FIG. 3, the image-forming apparatus 100contains a controller 50 that controls operations of the wholeimage-forming apparatus 100. The controller 50 includes a centralprocessing unit (CPU) 52, a read only memory (ROM) 54 and a randomaccess memory (RAM) 56. The CPU 52 carries out software (programs) readout of the ROM 54 to control each portion of the image-forming apparatus100 to realize any functions relating to thetoner-adhesion-amount-controlling mode and the image-forming processing.

To the controller 50, the manipulation/display portion 70, a storageportion 72, the image-forming portion 10, the fixing portion 44, the IDCsensor 110 and the image density sensor 120 are respectively connected.The manipulation/display portion 70 displays the menu screen or the likeon its screen based on a display signal or the like received from thecontroller 50 and produces a manipulation signal based on inputinformation received by the menu screen or the like and/or inputinformation by the manipulation keys to output it to the controller 50.

The storage portion 72 includes a nonvolatile semiconductor memory, harddisk drive (HDD) and the like. The storage portion 72 stores a tablestoring a plurality of the fixing temperatures, the developing voltagesand the like, which are used when performing thetoner-adhesion-amount-controlling mode, set values indicating the fixingconditions so that the patch is the fixity saturation state thereof, andthe like.

The image-forming portion 10 forms the patch which is a toner image forcontrolling the toner adhesion amount or the like on the intermediatetransfer belt 8 based on any control information received from thecontroller 50. The fixing portion 44 adjusts the fixing temperature ofthe heating rollers, pressure (nip pressure) by the pressure rollers anda transporting speed of the sheet P (rotation speed of the rollers) whenthe sheet P is passed through the fixing portion 44, based on anycontrol signals received from the controller 50.

The IDC sensor 110 irradiates the light based on any control signalsreceived from the controller 50 and outputs to the controller 50 thevoltage value based on the toner adhesion amount of the patch, which isdetected in the measurement. The image density sensor 120 irradiates thelight to the patch based on any control signals received from thecontroller 50 and outputs to the controller 50 the voltage value basedon the toner adhesion amount of the patch, which is detected in themeasurement.

[Example of Relationship Between Image Density and Fixing Temperature]

FIG. 4 shows the relationship between the fixing temperature and theimage density in the fixing processing. The vertical axis thereofindicates the image density and the horizontal axis thereof indicatesthe fixing temperature. In FIG. 4, a case A is shown in which the toneradhesion amount to the patch is set to become a standard amount; a caseB is shown in which the toner adhesion amount to the patch is set tobecome a large amount; and a case C is shown in which the toner adhesionamount to the patch is set to become a small amount. The following willdescribe the case A in which the toner adhesion amount to the patch isset to become the standard amount, as the representative example.

As shown in FIG. 4, when the temperature increases, the image density ofthe patch on the sheet P also increases. In this embodiment, in thestandard image-forming process, the fixing temperature in the realusable area is, for example, about 175° C. When the temperature furtherincreases, the image density is highest at the fixing temperature of,for example, 210° C., in which the image density is saturated. Thetemperature area near the highest value of the image density is also asaturation area in which the image density is not almost changed evenwhen the fixing temperature (fixing condition) is changed.

In this embodiment, a state in which the image density is not almostchanged even when the fixing condition (fixity) is changed is referredto as “fixity saturation state”. In other words, in the fixitysaturation state, an inclination of the image density with respect tothe fixing temperature is smaller than that of the real usable area.Specifically, when the image density is highest at the fixingtemperature of 210° C., the fixity saturation state appears at thetemperature area between 200° C. and 220° C. around the fixingtemperature of 210° C. Further, the temperature area in which the fixitysaturation state appears may be set so as to be a narrower or broaderarea than the above-mentioned temperature area if it is within a rangehaving a fixed fluctuation band.

On the other hand, when the fixing temperature still further increasesand exceeds the fixing temperature area in which the fixity saturationstate appears, the fixing temperature is excessive so that the toner isseparated from the sheet to generate any failure in image such asoff-set and a decrease in image density. It is to be noted that in casesB and C of the toner adhesion amounts, although the image densities aredifferent from that of the case A in the toner adhesion amount, theiroutput shapes of the toner adhesion amount are almost the same shapes asthat of the case A.

[Example of Relationship Between Image Density and Toner AdhesionAmount]

FIG. 5 shows the relationship between the fixing temperature and thetoner adhesion amount in the fixing processing. The vertical axisthereof indicates the image density and the horizontal axis thereofindicates the toner adhesion amount on the sheet. In FIG. 5, a thicksolid line indicates a case where the fixing condition is set to be Tawithin the real usable area and thick dotted lines indicate cases wherethe fixing conditions are changed to Tb and Tc within the real usablearea. A fine solid line indicates a case where the fixing condition isset to be Td within the fixity saturation state and fine dotted linesindicate cases where the fixing conditions are changed to Te and Tfwithin the fixity saturation state.

As shown in FIG. 5, when the toner adhesion amount to the patch on thesheet P increases, the image density of the patch also increases. Forexample, when the fixing temperature is set to be Ta within the realusable area and the toner adhesion amount is set to be X, the imagedensity is Da. Here, when the fixing temperature is changed from thetarget temperature Ta to temperature Tb or Tc based on any variations inthe installation condition of the image-forming apparatus, the imagedensity considerably changes. Therefore, when adjusting the variationsin the image density based on the variation in the fixing temperature bythe toner adhesion amount, there may be a case where the adjustment bythe toner adhesion amount is excessive or insufficient.

On the other hand, when the fixing temperature is set to be Td withinthe fixity saturation state and the toner adhesion amount is set to beX, the image density is Db. Here, when the fixing temperature is changedfrom the target temperature Td to temperature Te or Tf based on anyvariations in the installation condition of the image-forming apparatus,the image density does not almost changes as compared with the case ofthe real usable area. Namely, when the toner adhesion amount is fixed inthe fixity saturation state, the image density is univocally fixedwithout receiving any influence of the variation in the fixingtemperature. Thus, in this embodiment, any accurate toner adhesionamount may be adjusted, by utilizing the image density in the fixitysaturation situation, without receiving any influence of the variationin the fixing temperature.

[Operation Example of Image-Forming Apparatus]

The following will describe an operation example of the image-formingapparatus 100 according to the first embodiment of this invention withreference to FIGS. 6 through 10. FIG. 6 shows an operation example ofthe image-forming apparatus 100 in the first embodiment of thisinvention in the toner-adhesion-amount-controlling mode. Thetoner-adhesion-amount-controlling mode starts by, for example, theselection of a mode-starting button displayed on the screen of themanipulation/display portion 70.

As shown in FIG. 6, at a step S10, when starting thetoner-adhesion-amount-controlling mode, the controller 50 of theimage-forming apparatus 100 judges whether or not a determinationprocessing of fixity saturation state is performed to determine thefixing condition in which the image density of the patch is the fixitysaturation state. For example, the controller 50 judges whether or notthe determination processing of fixity saturation state is performedbased on whether or not an installation environment of the image-formingapparatus 100 or a use condition such as use history thereof is changedfrom the former determination processing time of the fixity saturationstate or the fixing portion 44 is exchanged. This is because the fixingconditions such as the fixing temperature are excessive when the imagedensity of the patch is saturated so that a phenomenon so-called “hotoff-set” in which the toner image transferred to the sheet P is toomelted to be adhered to the fixing portion 44, not to the sheet P, whichmay exert any bad influence upon the fixing portion 44. This is alsobecause it is desirable to decrease frequencies of fixing processing onthe fixity saturation state as much as possible. Therefore, in thisembodiment, the determination processing of fixity saturation state isperformed only when an individual difference occurs in the fixingportion 44 or the use condition of the image-forming apparatus 100 iseasy to vary and in this case, a new set value by which the imagedensity is the fixity saturation state is determined. For example, thecontroller 50 newly sets the set value when the fixing portion isexchanged. When judging that it is desirable that the determinationprocessing of fixity saturation state is performed, the controller 50goes to a step S20. When judging that it is desirable that thedetermination processing of fixity saturation state is not performed,the controller 50 goes to a step S30.

At the step S20, the controller 50 performs the determination processingof fixity saturation state. FIG. 7 is a subroutine showing an operationexample of the image-forming apparatus 100 in the determinationprocessing time of fixity saturation state at the step S20. As shown inFIG. 7, at a step S200, the controller 50 changes fixing conditions suchas the fixing temperature and pressure (nip pressure) of the fixingportion 44, and the transporting speed of the sheet P when the sheet Pis passed through the fixing portion 44 because the fixity is settled byheat to be added to the toner. The fixing condition is set to such avalue that, for example, the image density of the patch is the fixitysaturation state.

At a step S210, the controller 50 controls the image-forming portion 10and the like to print the patch(es) of solid patterns on the sheet P. Inthis embodiment, the controller 50 controls the image-forming portion 10and the like to print the black patch(es) on the sheet P. The fixingportion 44 performs the fixing process on the patch transferred to thesheet P by the secondary transfer rollers 34 under the fixing conditionset at the step S200.

At a step S220, the image density sensor 120 measures the image densityof the patch(es), which the fixing portion 44 fixes, on the sheet P andoutputs to the controller 50 an output value (voltage value) based on anamount of received light that is obtained by the measurement. Thecontroller 50 acquires the image density of the patch(es) based on theoutput value output from the image density sensor 120 and the storageportion 72 stores any information about the acquired image density ofthe patch(es). For example, the controller 50 acquires the image densityof the patch from the output value using an output characteristics graphindicating the previously set relationship between the image density andthe output value.

At a step S230, the controller 50 judges whether or not predeterminednumbers (for example, three through five) of patches are printed on thesheet P. The controller 50 goes to a step S240 when it judges that thepredetermined numbers of patches are printed on the sheet P. On theother hand, the controller 50 goes back to the step S200 when it judgesthat the predetermined numbers of patches are not printed on the sheetP. At the step S200, the controller 50 changes the fixing conditions,controls the fixing portion 44 to fix the patch(es) printed on the sheetP under the changed fixing conditions and controls the image densitysensor 120 to measure the image density of the patch(es). Suchprocessing is repeatedly performed until the predetermined numbers ofthe patches are printed.

At a step S240, the controller 50 judges that the fixing condition inwhich the image density is the highest image density among the obtainedimage densities of a plurality of patches is the fixing condition inwhich the image density of the patch is the fixity saturation state. Thecontroller 50 judges that this fixing condition is settled as the setvalue when the image density of the patch is the fixity saturationstate. Further, as the set value when the image density of the patch isthe fixity saturation state, a value near the highest value of the imagedensity may be used in addition to the highest value of the imagedensity (see FIG. 4). Namely, it is possible to use the value as the setvalue if the fixing conditions are within a range in which the imagedensity of the patch is not considerably changed based on the variationsin the fixing conditions. The storage portion 72 stores the settled setvalue. When settling the set value of the fixity saturation state, thecontroller 50 goes back to the step S30 shown in FIG. 6.

At the step S30, the controller 50 reads the set values out of thestorage portion 72 and sets the fixing temperature and pressure of thefixing portion 44, the transporting speed of the sheet P and the likebased on the read set value. When the controller judges at the step S10that the use conditions of the image-forming apparatus 100 are notchanged, the controller 50 also reads the set value, which has been usedbefore the variation in the use phenomenon of the apparatus or beforethe exchange of the fixing portion 44, out of the storage portion 72 andsets it as the fixing conditions.

At a step S40, the controller 50 performs a toner adhesion amountadjustment after the fixing conditions are set to a set vale so that theimage density of the patch is the fixity saturation state. FIG. 8 is asubroutine showing an operation example of the image-forming apparatus100 in the toner adhesion amount adjustment time.

As shown in FIG. 8, at a step S400, the controller 50 changes a targetvalue of the toner adhesion amount of the patch to be transferred to theintermediate transfer belt 8 (hereinafter, referred to as “target valueof the toner adhesion amount on the intermediate transfer belt”) ornewly sets it. Further, when forming the second patches or more, thecontroller 50 changes the target value of the toner adhesion amount onthe intermediate transfer belt to other one which is different from thatof the former patch forming time. For example, the controller 50 selectsany desired target values of the toner adhesion amount on theintermediate transfer belt by referring to a table in which pluraltarget values of the toner adhesion amount on the intermediate transferbelt have previously stored and set them as the target values of thetoner adhesion amount on the intermediate transfer belt.

At a step s410, after the controller sets the target values of the toneradhesion amount on the intermediate transfer belt, the controller 50performs a toner adhesion amount adjustment on the intermediate transferbelt to adjust the toner adhesion amount of the patch(es) to betransferred on the intermediate transfer belt 8. FIG. 9 is a subroutineshowing an operation example of the image-forming apparatus 100 in thetoner adhesion amount adjustment time on the intermediate transfer belt.As shown in FIG. 9, at a step S411, the controller 50 changes developingvoltages (image-forming conditions) in the developing portions 4. Forexample, the controller 50 selects desired developing voltages byreferring to a table in which a plurality of developing voltages havebeen stored and sets them as the desired developing voltages.

At a step S412, the controller 50 controls the developing portions 4 andthe like based on the changed developing voltages and control thetransfer portion to transfer the patch(es) of solid patterns on theintermediate transfer belt 8. In this embodiment, the controller 50controls the transfer portion to transfer the black patch(es) onnon-image-forming area of the intermediate transfer belt 8.

At a step S413, the IDC sensor 110 detects the toner adhesion amount ofthe patch(es) formed on the intermediate transfer belt 8 and outputs tothe controller 50 an output value based on the detected toner adhesionamount. The controller 50 acquires the toner adhesion amount of thepatch(es) based on the output value output from the IDC sensor 110 andthe storage portion 72 stores any information on the acquired toneradhesion amount.

At a step S414, the controller 50 judges whether or not predeterminednumbers (for example, three through five) of patches are printed on theintermediate transfer belt 8. The controller 50 goes to a step S415 whenit judges that the predetermined numbers of patches are printed on theintermediate transfer belt 8. On the other hand, the controller 50 goesback to the step S411 when it judges that the predetermined numbers ofpatches are not printed on the intermediate transfer belt 8. At the stepS411, the controller 50 changes the developing voltages in thedeveloping portions 4 and controls the transfer portion to transfer thepatch(es), the toner adhesion amount of which is different from theformer amount, on the intermediate transfer belt 8 under the changeddeveloping voltages. Such processing is repeatedly performed until thepredetermined numbers of the patches are transferred.

At a step S415, after the predetermined numbers of the patches aretransferred, the controller 50 sets an optimal developing voltage thatis the set target value of the toner adhesion amount on the intermediatetransfer belt from the relationship between the developing voltages inthe developing portions 4 and the toner adhesion amount (output value)detected by the IDC sensor 110. For example, the controller 50calculates an approximation from the developing voltage and toneradhesion amount acquired for every patch and sets the developing voltagecorresponding to the target value of the toner adhesion amount on theintermediate transfer belt from the calculated approximation. Thecontroller 50 goes to a step S420 shown in FIG. 8 from the subroutineafter the optimal developing voltage is set.

At the step S420, the controller 50 controls the developing portions 4and the like to print the patch of solid patterns on the sheet P basedon the developing voltage set at the step S415. In this embodiment, thecontroller 50 controls the developing portions 4 and the like to printthe black patch(es) on the sheet P. The fixing portion 44 performs thefixing process on the patch(es) printed on the sheet P under the fixingconditions set at the step S30 so that the image density of the patch isthe saturation state.

At a step S430, the image density sensor 120 measures the image densityof the patch(es), which the fixing portion 44 fixes, on the sheet P andoutputs to the controller 50 an output value based on the detected imagedensity. The controller 50 acquires the image density of the patch(es)based on the output value output from the image density sensor 120 andthe storage portion 72 stores any information about the acquired imagedensity of the patch(es). For example, the controller 50 calculates theimage density of the patch(es) from the output value acquired by theimage density sensor 120 using an output characteristics graph(approximation) indicating the previously set relationship between theimage density and the output value.

At a step S440, the controller 50 judges whether or not predeterminednumbers (for example, three through five) of patches are printed on thesheet P. The controller 50 goes to a step S450 when it judges that thepredetermined numbers of patches are printed on the sheet P. On theother hand, the controller 50 goes back to the step S400 when it judgesthat the predetermined numbers of patches are not printed on the sheetP. At the step S400, the controller 50 changes the target value of thetoner adhesion amount on the intermediate transfer belt and acquires theoptimal developing voltage corresponding to the changed target value ofthe toner adhesion amount on the intermediate transfer belt. Suchprocessing is repeatedly performed until the predetermined numbers ofthe patches are printed.

At the step S450, the controller 50 sets the optimal target value of thetoner adhesion amount on the intermediate transfer belt from therelationship between the target value of the toner adhesion amount onthe intermediate transfer belt and the image density of the patch(es)printed under this target value. For example, the controller 50calculates the relationship between the target value of the toneradhesion amount on the intermediate transfer belt and the image density,which are acquired for every patch, and acquires the target value of thetoner adhesion amount on the intermediate transfer belt corresponding tothe image density as the target value thereof from the calculatedrelationship. As one example thereof, when describing it using FIG. 5,if the toner adhesion amount on the sheet (the target value of the toneradhesion amount on the intermediate transfer belt) is X, the imagedensity as the target value thereof can be set to Db.

At a step S460, after the controller 50 sets the optimal target value ofthe toner adhesion amount on the intermediate transfer belt, thecontroller 50 again performs the toner adhesion amount adjustment on theintermediate transfer belt of the steps S411 through S415 shown in FIG.9. This enables the optimal developing voltage corresponding to thetarget value of the toner adhesion amount on the intermediate transferbelt acquired at the step S450 to be set and enables the toner adhesionamount of the image to be printed on the sheet P to be adjusted to thetarget value thereof. After the developing voltage is set, thecontroller 50 goes to a step S50 shown in FIG. 6.

At the step S50, the controller 50 performs fixity adjustment. Namely,since the toner adhesion amount of the patch(es) on the sheet P can beset so as to be the target value thereof, the fixing temperature is nextadjusted to a normal value thereof when the fixing temperature isdifferent therefrom. FIG. 10 is a subroutine showing an operationexample of the image-forming apparatus 100 in the fixity adjustment timeat the step S50. As shown in FIG. 10, at a step S500, the controller 50changes fixing temperature of the fixing portion 44. For example, thecontroller 50 changes the fixing temperature of the fixing portion 44 byreferring to a table in which a plurality of fixing temperatures hasbeen previously stored.

At a step S510, the controller 50 controls the image-forming portion 10and the like to print the patch(es) of solid patterns on the sheet P. Inthis embodiment, the controller 50 controls the image-forming portion 10and the like to print the black patch(es) on the sheet P. The controller50 then sets the fixing conditions to the fixing temperature that is thetarget value in the real usable area which, for example, is used in thenormal image-forming process time. This enables the fixing process to beperformed on the patch(es) printed on the sheet P at the set fixingtemperature.

At a step S520, the image density sensor 120 measures the image densityof the patch(es), which the fixing portion 44 fixes, on the sheet P andoutputs to the controller 50 an output value (voltage value) based onthe detected image density. The controller 50 acquires the image densityof the patch(es) corresponding to the output value output from the imagedensity sensor 120 and the storage portion 72 stores any informationabout the acquired image density of the patch(es).

At a step S530, the controller 50 judges whether or not predeterminednumbers (for example, three through five) of patches are printed on thesheet P. The controller 50 goes to a step S540 when it judges that thepredetermined numbers of patches are printed on the sheet P. On theother hand, the controller 50 goes back to the step S500 when it judgesthat the predetermined numbers of patches are not printed on the sheetP. At the step S500, the controller 50 changes the fixing temperature,controls the fixing portion 44 to fix the patch(es) at the changedfixing temperature and controls the image density sensor 120 to measurethe image density of the fixed patch(es). Such processing is repeatedlyperformed until the predetermined numbers of the patches are printed.

At a step S540, the controller 50 selects the fixing temperaturecorresponding to the target image density based on the relationshipbetween the fixing temperature and the image density and sets it as theoptimal fixing temperature. This enables the fixing temperature to beaccurately adjusted. It is also possible to control the image density ofthe patch(es) so as to be its (their) set target value. Further,although the fixing temperature has been adjusted as the fixingconditions in this embodiment, the invention is not limited thereto: Itis possible to adjust the nip pressure of the fixing portion 44 and/orthe transporting speed of the sheet P.

As described above, since the image-forming apparatus 100 according tothe first embodiment performs the toner-adhesion-amount-controlling modeat the fixing conditions so that the image density is the fixitysaturation state, it is possible to control the toner adhesion amountaccurately without exerting any influence of the variations in thefixing portion 44. This prevents generating any failure in fixingseparation and the like when the toner adhesion amount is excessive.This also prevents generating any various kinds of failure in the imagesuch as density unevenness, deterioration of graininess and the likewhen the toner adhesion amount is insufficient. A fixing control by aglossiness sensor is not required so that the costs therefor are reducedand miniaturization of the image-forming apparatus 100 can be realized.

Further, in the first embodiment, the toner-adhesion-amount-controllingmode according to this invention is not performed in all of the processvariations in the transfer portion and/or the fixing portion 44. Thetoner-adhesion-amount-controlling mode is performed on the detection ofthe toner adhesion amount of the image on the sheet P and on the timewhen a factor influencing the fixity is changed and the like. Normally,the toner adhesion amount is controlled using the intermediate transferbelt 8. This prevents waste paper from being generated and productivityof the image-forming apparatus 100 from being reduced.

Additionally, in the first embodiment, since the fixity saturation stateis set in a case where the individual difference varies when the fixingportion 44 is exchanged or the use condition of the image-formingconditions varies in the determination processing of the fixitysaturation state of the toner-adhesion-amount-controlling mode, it ispossible to reduce a case where the fixity is excessive. This avoids theoff-set in which the toner is too molten so that it is adhered to thefixing portion 44, not the sheet P.

Second Embodiment

The following will describe an image-forming apparatus according to asecond embodiment of this invention in which thetoner-adhesion-amount-controlling mode is performed without using anyintermediate transfer belt 8. It is to be noted that otherconfigurations and operations of this image-forming apparatus accordingto the second embodiment are similar to those of the image-formingapparatus according to the first embodiment so that like numbersindicate like components in this embodiment, the detailed description ofwhich will be omitted.

The following will describe the operations of the image-formingapparatus 100 according to the second embodiment that performs thetoner-adhesion-amount-controlling mode with reference to FIG. 6. Theoperations of the steps S10, S20, S30 and S50 shown in FIG. 6 aresimilar to those of the first embodiment and they will be brieflydescribed.

First, at the step S10 shown in FIG. 6, the controller 50 judges whetheror not a determination processing of fixity saturation state isperformed to determine the fixing condition so that the image density ofthe patch is the fixity saturation state. When judging that it isdesirable that the determination processing of fixity saturation stateis performed, the controller 50 goes to the step S20. At the step S20,the controller 50 performs the determination processing of fixitysaturation state and sets the fixing conditions in the fixing portion 44so that the image density of the patch is the fixity saturation state.

After the controller 50 sets the fixing conditions to the set values ofthe fixity saturation state, the controller 50 performs the toneradhesion amount adjustment. FIG. 11 is a subroutine showing an operationexample of the image-forming apparatus 100 according to the secondembodiment in the toner adhesion amount adjustment time. As shown inFIG. 11, at a step S600, the controller 50 changes developing voltagesin the developing portions 4.

At a step S610, the controller 50 controls the developing portions 4 andthe like based on the changed developing voltages and control theimage-forming portion 10 and the like to print the patch(es) of solidpatterns on the sheet P. This allows the fixing process to be performedon the patch(es) printed on the sheet P under the fixing conditions setat the step S30.

At a step S620, the image density sensor 120 detects the image densityof the patch(es) formed on the sheet P, which the fixing portion 44fixes, and outputs to the controller 50 an output value based on thedetected image density. The controller 50 acquires the image density ofthe patch(es) based on the output value output from the image densitysensor 120 and the storage portion 72 stores any information on theacquired image density of patch(es).

At a step S630, the controller 50 judges whether or not predeterminednumbers (for example, three through five) of patches are printed on thesheet P. The controller 50 goes to a step S640 when it judges that thepredetermined numbers of patches are printed on the sheet P. On theother hand, the controller 50 goes back to the step S600 when it judgesthat the predetermined numbers of patches are not printed on the sheetP. At the step S600, the controller 50 changes the developing voltagesin the developing portions 4, controls the fixing portion 44 to fix thepatch(es) printed on the sheet P based on the changed developingvoltages, and controls the image density sensor 110 to detect the imagedensity of the fixed patch(es). Such processing is repeatedly performeduntil the predetermined numbers of the patches are transferred.

At the step S640, the controller 50 sets an optimal developing voltageof the developing portions 4 from the relationship between thedeveloping voltages in the developing portions 4 and the image densityof the patch(es) printed under the developing voltages. For example, thecontroller 50 calculates an approximation from the developing voltageand the image density acquired for every patch and sets the optimaldeveloping voltage corresponding to the target value of the imagedensity (toner adhesion amount) using the calculated approximation. Thisenables the optimal toner adhesion amount to be acquired as the targetvalue thereof on the sheet P.

The controller 50 then goes to the step S50 where the controller 50 setsthe optimal developing voltage in the toner-adhesion amount adjustmentand goes to the steps S500 through S540 shown in FIG. 10 where thecontroller 50 performs the fixity adjustment.

As described above, the image-forming apparatus 100 according to thesecond embodiment has the same effects as those of the first embodiment.Namely, according to this second embodiment, since thetoner-adhesion-amount-controlling mode is performed at the fixingconditions so that the image density is the fixity saturation state, itis possible to control the toner adhesion amount accurately withoutexerting any influence of the variations in the fixing portion 44. Thisprevents generating any failure in fixing separation and the like whenthe toner adhesion amount is excessive. This also prevents generatingany various kinds of failure in density unevenness, deterioration ofgraininess and the like when the toner adhesion amount is insufficient.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.Although, in the above-mentioned embodiments, the set value so that theimage density is the fixity saturation state has been obtained when thetoner-adhesion-amount-controlling mode is selected, this invention isnot limited thereto: For example, any optimal set value so that theimage density is the fixity saturation state may be acquired by anexperiment; Any optimal set value so that the image density is thefixity saturation state may be estimated from the pat use conditions;The storage portion 72 may store these set values previously, before theshipment thereof. This allows the image density of the patch(es) to besaturation state even when the image-forming apparatus having lessvariation in its use condition performs any image-forming process. Thus,it is possible to control the toner adhesion amount accurately.

Further, although the developing voltages of the developing portions 4have been adjusted in the toner adhesion amount adjustment on theintermediate transfer belt 8 to control the toner adhesion amount of thepatch(es) formed on the sheet P, this invention is not limited thereto:For example, it is possible to control the toner adhesion amount of thepatch(es) by adjusting at least one of the image-forming conditions suchas voltage or current of the charging portions 2, voltage or current ofthe exposure portions 3, and voltage or current of the transfer portionsuch as the secondary transfer rollers 34.

1. An image-forming apparatus comprising: an image-forming portion thatforms a patch on a sheet, the patch being a tonner image; a fixingportion that fixes the patch formed by the image-forming portion on thesheet; an image-density-detecting portion that detects an image densityof the patch fixed by the fixing portion on the sheet; and a controllerthat controls the fixing portion to control a toner adhesion amountbased on a detection result of the image density of the patch by theimage-density-detecting portion, wherein the controller sets a fixingcondition of the fixing portion in the control so that the image densityof the patch is saturated and controls the fixing portion to control thetoner adhesion amount based on the detection result of the image densityof the patch by the image-density-detecting portion, the patch beingformed under the set fixing condition.
 2. The image-forming apparatusaccording to claim 1 wherein the controller controls the fixing portionto fix plural patches under different fixing conditions, and sets as aset value of the fixing condition in which the image density of thepatch is saturated a fixing condition in which the image density ishighest or approximate to the highest value of the plural patchesdetected by the image-density-detecting portion.
 3. The image-formingapparatus according to claim 2 wherein the controller newly sets the setvalue when a use condition of the image-forming apparatus varies from aformer setting time of the set value.
 4. The image-forming apparatusaccording to claim 2 wherein the controller newly sets the set valuewhen the fixing portion is exchanged.
 5. The image-forming apparatusaccording to claim 1 wherein a set value of the fixing condition so thatthe image density of the patch is saturated is previously set.
 6. Theimage-forming apparatus according to claim 1 wherein the fixingcondition is at least one condition of a fixing temperature, pressure,and a transporting speed of the sheet during a passing time through thefixing portion.
 7. The image-forming apparatus according to claim 1wherein the image-forming portion contains a charging portion, adeveloping portion, an exposing portion and a transferring portion; thecontroller controls the toner adhesion amount of the patch formed on thesheet by adjusting at least one condition of voltage/current in thecharging portion, a developing voltage in the developing portion,voltage/current in the exposing portion, and voltage/current in thetransferring portion.
 8. The image-forming apparatus according to claim1 wherein the image-forming portion contains image carrier that carriesthe toner image and an adhesion amount detection portion that detectsthe toner adhesion amount of the patch formed on the image carrier; andthe controller sets an image-forming condition based on the toneradhesion amount of the patch detected by the adhesion amount detectionpart, and then, controls the toner adhesion amount so that the toneradhesion amount on the image carrier is a set target value based on theimage density of the patch formed under the set image-forming condition.9. The image-forming apparatus according to claim 1 wherein thecontroller controls the toner adhesion amount and then, sets a fixingcondition of the fixing portion based on the detection results of theimage densities of the plural patches formed under the plural fixingconditions so that the image densities of the patches are the set targetvalue.